1. Field of the Invention
The present invention relates to a valve assembly and more particularly to a pneumatic pressure control valve assembly operative in response to and utilizing both positive and negative fluid pressures as control signals.
2. Prior Art
Various systems and devices have recently been proposed for emission control for vehicles in which valve assemblies responsive to an intake manifold vacuum signal downstream of the throttle valve are incorporated. In a particular prior system, the valve assembly must satisfy the requirement wherein the valve member closes (or opens) the fluid passage during engine idling and opens (or closes) the fluid passage during engine deceleration. Normally, the manifold vacuum during engine deceleration is higher than that during engine idling, however, the reverse condition of relative vacuum may occur due to various adjustment problems, such as operational adjustments of engine intake and exhaust valves. Therefore, it may be possible that the above requirement can not be satisfied.
For example, when the valve assembly is adapted to control the operation of a fuel regulator having main and slow fuel supply lines, it is desirable that the valve assembly assures the fuel supply of both main and slow lines during engine idling, but the valve assembly closes the fuel supply of the slow line during engine deceleration. In an L.P.G. vehicle wherein the fuel can be sufficiently drawn in by increasing the opening of the throttle valve, the supply of fuel may be in proportion to the change in the degree of opening of the throttle valve. In order to avoid the undesirable stopping of the engine especially during engine idling, the supply of fuel through the slow fuel line as well as the main fuel line is necessary. The slow fuel line should be closed during engine deceleration to prevent damage to the catalytic converter and reduce HC, CO in the exhaust gas.
Similarly, the controlled output of fluid through the valve assembly may be transmitted to the intake manifold. By means of such a valve assembly, air is introduced into the manifold during engine deceleration to reduce HC and CO within the exhaust gas and to prevent backfire of the engine, but introduction of air is stopped during engine idling to avoid the undesirable stopping of the engine.
In summary, it is possible that the desirable controlled output pressure can not be produced in the prior valve assembly utilizing only manifold vacuum pressure as a control signal. It should be noted that vacuum pressure at the intake manifold is variable in response to the altitude or the environment in which the engine is operating.